Historically, flexible intermediate bulk containers (bulk bags) have been used for receiving, storing, transporting and discharging flowable materials of all types. Bulk bags are typically constructed in square, vertically rectangular, or circular shapes with lift straps attached to each of the uppermost corners of the square, rectangle or circle.
By way of example, flexible intermediate bulk containers are used for handling flowable materials in granular or powder form such as chemicals, minerals, fertilizers, foodstuffs, grains and agricultural products, etc. The advantages of such receptacles include relatively low weight, reduced cost, versatility and, in the case of reusable receptacles, low return freight costs.
At the present time most bulk bags are manufactured from woven polypropylene fabric. Typically, such containers comprise two or more sidewalls and a bottom portion. Optionally, a top wall and lift straps or other lifting members can be added to the basic construction. The traditional method of securing the seams of the several portions of a bulk bag includes sewing or stitching.
Bulk bags are frequently provided with liners, which may be installed either during or after the manufacture of the bulk bag itself. Liners are used to prevent material contained in the bag from sifting through the woven polypropylene comprising the bag and/or through the sewn seams which are used in construction of the bag. Examples of liners for bulk bags are described in U.S. patent applications Ser. Nos. 08/417,898; 08/383,887; and 08/619,419, each assigned to the Assignee of the present application. Liners may also be used to provide bulk bags with improved anti-static, anti-corrosion and/or anti-microbial characteristics. See, for example, U.S. patent application Ser. No. 08/474,378, filed Jun. 7, 1995 for ANTI-STATIC, ANTI-CORROSION, AND/OR ANTI-MICROBIAL FLEXIBLE COLLAPSIBLE RECEPTACLES and assigned to the Assignee of the present application.
One problem that has long been associated with the use of liners in bulk bags comprises the tendency of liners to move or shift relative to the bulk bag in which they are used. In extreme instances, the discharge of material from a bulk bag may cause a liner disposed therein to pull completely out of the bulk bag through its discharge opening. The problem of liner displacement has been addressed previously; for example, see U.S. Pat. No. 4,597,102 granted to Nattrass on Feb. 24, 1986 and U.S. Pat. No. 4,781,472 granted to La Fleur, et al. on Nov. 1, 1988. However, despite these and other attempts at preventing the displacement of liners relative to the bulk bags in which they are installed, a need exists for still further improvement in the art.
Another problem associated with prior art liners comprises the possibility of dirt and other contaminants sifting through the top or sides of the woven fabric and then collecting between the exterior bag and the impermeable liner. In prior art bags, when the liner contents are discharged the liner collapses because it is not affixed effectively to the exterior bag. As the liner collapses during discharge, the dirt and contaminants collected between the exterior bag and the interior liner may be discharged through the annular space between the bag discharge chute and the liner along with the product being discharged from the liner. Thus, a need exists for an effective safety seal on the top of the liner to prevent contaminants from being discharged with the product when the liner is emptied.
Yet another problem associated with prior art bulk bags and liners is their lack of conductivity. Friction that occurs as dry flowable materials are discharged from woven bags tends to cause a significant build up and retention of static electric charge within the receptacle. Discharge of the generated static electric build-up is often difficult if not impossible to control because fabrics are generally not electrically conductive materials. In an effort to address the undesirable characteristics of fabrics, prior art methods have included covering one side of the fabric with a metallic foil-like layer. While adequate in discharging static electric charge, the foil was susceptible to abrasion and tearing through use. Subsequent prior art methods include impregnating the fabric fibers with conductive elements to make the fabric itself conductive. Despite these and other attempts, a need continues to exist for a safe and cost effective solution to the problem of static electric build up in bulk bags.